1. Field of the Invention
The invention relates to a process of producing coarse-grain crystalline and/or monocrystalline metal and alloy films and somewhat more particularly to a process of producing coarse-grain crystalline or monocrystalline metal or alloy films on substrates composed of ceramic, glass or silicon by conversion of an amorphous metallic film on such substrate into a coarse-grain crystalline or monocrystalline state.
2. Prior Art
Metal or alloy films on substrates composed of ceramic, glass or silicon are frequently used in electrical technology. Such thin metal films function, for example, as conductor path structures, electrical resistors or capacitors in semiconductor technology. Such metal films, which are employed in thin film technology, are frequently subjected to relatively high thermal stresses, with continuous loads of approximately 150.degree. C. and intermittent loads of approximately 400.degree. C. Despite such stresses, the stability of the film characteristics over prolonged periods of time, especially the electrical characteristics thereof, must be guaranteed.
Metal films are typically produced on substrates composed of glass, ceramic or silicon, via, for example, "atomization" (sputtering) or vapor-deposition and typically assume a finely crystalline form. At elevated temperatures, an uncontrolled growth of the crystallites can start, which in many instances can lead to significant changes in the film characteristics.
The prior art is aware that stabilization of metal films can be obtained by annealing such films at higher temperatures (ie., wherein T is greater than 400.degree. C.). However, such high-temperature annealing can be very unfavorable in semiconductor-IC structures since the electrical components which are already present on a substrate can be substantially changed by the annealing temperature, because, for example, in the case of metal conductor paths, during the occurence of uncontrolled crystal growth, grain boundaries can arise crosswise or perpendicular to a conductor path. Such grain boundaries substantially raise the failure rate of a conductor path since mass transport of material by means of electron migration occurs via such boundaries, for example see Thin Solid Films, Vol. 16, pages 227-236 (1973).
German Offenlegungsschrift (hereinafter DE-OS) No. 27 27 659 suggests that monocrystalline thin metal films can be produced from amorphous metal films on substrates composed of ceramic, glass or silicon by thermally converting the amorphous film or layer into a monocrystalline state.
In accordance with this method, stable film characteristics are attained by depositing metal layers or films, preferably composed of tantalum, onto low temperature substrates, for example having -160.degree. C. on the deposition surface, so that the deposited film is in an amorphous or greatly disordered form and thereafter crystallizing such amorphous film by very slightly heating the substrate. In this manner, coherent lattice spaces are enlarged from less than about 4 nm during deposition on the substrate up to crystals having a grain diameter of at least 70 .mu.m upon heating the substrate up to about -90.degree. C. Such films maintain their relevant characteristics at even much, much higher temperatures (ie., higher than +400.degree. C.) even though during their fabrication process, they are exposed to no temperature higher than about -90.degree. C.